Currently, batteries, for example, Lithium-Ion batteries, are widely used to provide power supply to a variety of electronic devices or systems, such as notebook computers, electric vehicles (EVs), hybrid electric vehicles (HEVs), and power tools. A circuit is typically used to control charging and/or discharging of a battery pack.
FIG. 1 shows a conventional circuit 100 for controlling charging and discharging of a battery pack. The battery pack includes a battery 110 and terminals PACK+ and PACK−. The circuit 100 includes a discharge metal-oxide-semiconductor field-effect transistor (MOSFET) 142, a charge MOSFET 122, a trickle discharge MOSFET 144, a trickle charge MOSFET 124, a resistor 184, a resistor 186, and a protection circuit (e.g., a protection integrated circuit (IC)) 160.
During charging, a charger is coupled to the terminals PACK+ and PACK− to charge the battery 110. In a normal charging mode, the charge MOSFET 122 controls a charging current. In a trickle charging mode, e.g., when the battery 100 is over drained, the trickle charge MOSFET 124 is fully on to allow a relatively small charging current to charge the battery 100 to prevent the battery pack from being damaged. The resistor 186 is used to limit the level of the charging current in the trickle charging mode. Typically, the charging current in the trickle charging mode is called a trickle charging current.
During discharging, the battery 110 is discharged to power a load coupled to the terminals PACK+ and PACK−. The discharge MOSFET 142 controls a discharging current in a normal discharging mode. In a trickle discharging mode, e.g., to avoid inrush current to the load or to detect the load condition when an open circuit or short circuit condition occurs to the load, the trickle discharge MOSFET 144 is fully on to allow a relatively small discharging current to flow to the load. The resistor 184 is used to limit the discharging current in the trickle discharging mode. Typically, the discharging current in the trickle discharging mode is called a trickle discharging current.
Since at least four MOSFETs are used, the circuit 100 may have a relatively high cost. Moreover, each of the MOSFETs 122, 124, 142 and 144 is driven separately by an individual driver in the driver block 162. In other words, the driver block 162 has to include several drivers and the protection IC 160 (which the driver block 162 is assembled into) may have a large pin count to drive the MOSFETs, which increases the cost of the protection IC 160. Furthermore, the voltage across the battery 110 increases as the trickle charging proceeds and thus the voltage across the resistor 186 drops. Therefore, the trickle charging current decreases, which results in a longer charging process.